Why go wider??

[BRGT350]

Do you know 100% the extra holes are ok from a safety standpoint? To me, that is a pretty bold statement that needs some facts to back that up. I would think the holes are probably ok, but I wouldn't do the modification to my ST. Decreasing the bolt circle reduces the clamp load area on the hub by around 9%, which will increase stress in the hub. Force is the same, but area decreases, therefore stress must increase. Increasing stress into a part that just got 4 additional holes added to it seems like a bad idea. I have become more cautious over time after being around a test lab in which you see what happens when parts fail. Sometimes small changes result in very unexpected failures. I have no interest in going down that road with my car.

 

[jeffreylyon]

in terms of efficiency, a 8" wide wheel is the opposite direction you want to go. It is wider, most likely heavier, offers more aerodynamic drag, requires a wider tires which is also heavier and has more drag. Heavier wheels and tires require more torque (both acceleration and brake) to overcome inertia. Require additional damping due to the unsprung weight increase. I would go with a 7" wide wheel and a very aggressive tire compound. Take the money saved and go to a driver's school and find out that with better techniques, you won't be running out of traction with a 7" wide wheel and a 215mm (or even a 205mm) wide tire. On the street, you should never even come close to overcoming the traction of the stock ST. On the track, you should be working on practice and driver education and not lap times. Fast lap times are 90% driver and 10% car. Go for a ride in a production car with a professional driver and you will see what I mean. One of the most incredible rides in my life came from a car with 140ish horsepower, but with a professional driver. No tire size in the world could give me the amount of traction that is gained from a driver who understands exactly how to control a car.

For sure, the best money spent is spent on the driver. Having said that, I lost 8#/corner on 17x8's that are lighter than any 17x7 I could find. On A/C tracks, the added aero drag on a Street classed car by going to a 1" wider wheel is completely negligible.

 

[BRGT350]

agree, that the aero drag is negligible. The OP did say he was seeking the most efficient, so that is why I included the point. You could probably alter the drag of the car more by adding a coat of wax more than the tire width increase. The decrease in unsprung weight is great! I would still argue that the money spent on lightweight wheels would be best spent on driver education, since that is where the most amount of time is lost on the track. When you get to a point in which you are done shaving seconds off of your lap due to inconsistency in the driver, then it is prime time for modifications. I don't get out to the track enough to be at that point anymore. I used to go every other week in the summer to the track and really hone my skills. That was years ago and now I am lucky to get out once a year. With that, I still say the best modification I made was to the driver and not any of the cars I have modified. Even the 1-day rally school taught me all sorts of skills that made a huge difference on the street and autocrossing. With a stock ST after the school, I was .2 seconds from taking a GS class win. That is the closest to winning a stock class I have ever been. Before the school with the same car, I was a mid-pack driver at best.

 

[jeffreylyon]

Do you know 100% the extra holes are ok from a safety standpoint? To me, that is a pretty bold statement that needs some facts to back that up. I would think the holes are probably ok, but I wouldn't do the modification to my ST. Decreasing the bolt circle reduces the clamp load area on the hub by around 9%, which will increase stress in the hub. Force is the same, but area decreases, therefore stress must increase. Increasing stress into a part that just got 4 additional holes added to it seems like a bad idea. I have become more cautious over time after being around a test lab in which you see what happens when parts fail. Sometimes small changes result in very unexpected failures. I have no interest in going down that road with my car.

Absolutely - the best way to ensure that your car is as safe as when it was delivered to you is to leave it completely alone. Any performance modification will increase stress. That being said, many of us chose to modify our cars and, in the process, assume the related risk.

And, to your point, the smaller bolt circle may decrease the load area but, really, the load area is determined by the area in which the two surfaces are in contact if the wheel nuts are torqued correctly. My brake hats are larger in diameter than both the inner face of my wheels or the outer face of my hubs - I'm pretty sure that all of the hub face is being loaded. But you're right, I'd need a mechanical engineer and/or a lab to guarantee that.

 

[BRGT350]

and as long as the risk is understood, that is ok. I don't know how many understand the risk, and I really didn't really understand it until getting my engineering degree and working as an engineer for years with much of that in suspension systems. There are many small factors that can alter the design intent in ways the engineers never intended. The hub and wheel connection is managed with clamp load from the lug nuts and studs with the applied torque. Surface area contact between the hub, brake hat, and wheel surface. Hub diameter and wheel hub for vertical loading, and the bolt circle area. By moving the studs further from center, you do increase the torque (not tightening torque, but reactive torque) on each stud that reacts to the acceleration and braking force. Does a 4mm radial reduction really make a significant difference, probably not.

 

[Gun_Runner]

Do you know 100% the extra holes are ok from a safety standpoint? To me, that is a pretty bold statement that needs some facts to back that up. I would think the holes are probably ok, but I wouldn't do the modification to my ST. Decreasing the bolt circle reduces the clamp load area on the hub by around 9%, which will increase stress in the hub. Force is the same, but area decreases, therefore stress must increase. Increasing stress into a part that just got 4 additional holes added to it seems like a bad idea. I have become more cautious over time after being around a test lab in which you see what happens when parts fail. Sometimes small changes result in very unexpected failures. I have no interest in going down that road with my car.

Absolutely - the best way to ensure that your car is as safe as when it was delivered to you is to leave it completely alone. Any performance modification will increase stress. That being said, many of us chose to modify our cars and, in the process, assume the related risk.

And, to your point, the smaller bolt circle may decrease the load area but, really, the load area is determined by the area in which the two surfaces are in contact if the wheel nuts are torqued correctly. My brake hats are larger in diameter than both the inner face of my wheels or the outer face of my hubs - I'm pretty sure that all of the hub face is being loaded. But you're right, I'd need a mechanical engineer and/or a lab to guarantee that.

I am a machinist, and have been for 10+ years, in a field with much more stringent requirements than anything that we are doing with our cars. This modification is in no way, shape or form more stressful on any component of the car. There are a lot of aspects of your reduced bolt circle diameter that did not get brought up in your argument.

The bolt circle is being reduced to 100mm rather than 108mm, BUT the outer diameter of the hub is not being reduced. This means that you are actually increasing the distribution of force from the wheel studs over a larger surface area. If the hub was going to fail in any direction, it is going to fail at its thinnest point, which was the the distance from the edge of the stud hole, to the edge of the hub. This modification almost doubles that distance. I can bet that if you put a hub into the stress testing system on solidworks, or other similar software, that you will actually see a decrease in overall stress. This will be further reinforced by the addition of light wheels that almost inevitably come with the modification.

If you want real world examples, go take a look at all of the cars out there that are larger and heavier than the Fiesta, and ill bet you that those cars even have a smaller hub diameter. In case it comes up, the argument of "Well, Ford must have picked 4x108 rather than 4x100 for some reason" is a stupid one. They use that pattern, simply because it is a pattern that they have used for a long time. Go take a look at how many rally cars there are out there, and tell me that we are putting even 50% of the stress on the hubs that those guys are throwing at them daily. Lastly, my father has been running a 1985 Dodge Omni with re-drilled rotors for almost 30 years. Those hubs have 300,000 plus miles on them, well over 2000 drag launches from 6000+ rpm running FAT slicks, and thousands of miles of road racing, coming from a car that puts out just shy of 400hp and 425ft/lbs to the wheels. Those hubs are smaller diameter than ours, and his hubs are re-drilled from a 5x100 hubs

If you have any more questions about that mod, i can answer them.

 

[BRGT350]

I see your point about the area around the stud increasing in relation to the edge of the hub. The OD stays the same, but the studs move away from the edge. You are right that the thinnest cross section is the weakest point. I also agree that your real world data does suggest there won't be an issue. While not a modification I am going to do, chances are fine others will be ok with the modification.

 

[Gun_Runner]

I see your point about the area around the stud increasing in relation to the edge of the hub. The OD stays the same, but the studs move away from the edge. You are right that the thinnest cross section is the weakest point. I also agree that your real world data does suggest there won't be an issue. While not a modification I am going to do, chances are fine others will be ok with the modification.

Sorry if it seemed like I went aggro on you in that last post, but I get a lot of people that will tell me that my mod is dangerous, with no logical backing. This is then usually shortly followed by them installing big adapter spacers, which are ACTUALLY dangerous, and detrimental to performance and durability. I like to keep pictures of exploded adapter spacers, for those guys.


The other thing I wanted to address, that someone else brought up earlier, was knowing something you are modifying is causing stress to a safety component, and just accepting that as known risk.

This is a terrible idea that no one should do or accept. We all understand that putting a huge turbo on a 1.6 adds stress to the engine components, and you risk damage to the engine. This is fine, because new pistons can always be bought (and probably should have been before the big turbo, lol).
When you make a modification that takes away an aspect of safety, a modification that increases the car's safety by an equal amount should be made. For example, professional drag cars put tiny, light weight brakes on their cars for weight reduction and balance, but when they do this, they also install a parachute, as well as a roll cage. Get me? This is why I hate the "stanced" movement. It is dangerous, and detrimental to performance.

I quite often refuse to do bolt pattern conversions for guys, because they want a 4x112 pattern, and it only leaves 1.22mm of sidewall before the OD. I probably could have done 20 more of these conversions if I didn't care about other's safety.

 

[M-Sport fan]

Go take a look at how many rally cars there are out there, and tell me that we are putting even 50% of the stress on the hubs that those guys are throwing at them daily.

Absolutely true, but, it is a pretty safe bet that those cars do NOT have an extra set of holes drilled into the hub flanges, AND they are all converted to 5 lug hubs as well.

When you supply the hardware for this conversion, do you at least chamfer/stress relieve the new, drilled, stud holes?

 

[M-Sport fan]

Do you know 100% the extra holes are ok from a safety standpoint? To me, that is a pretty bold statement that needs some facts to back that up. I would think the holes are probably ok, but I wouldn't do the modification to my ST. Decreasing the bolt circle reduces the clamp load area on the hub by around 9%, which will increase stress in the hub. Force is the same, but area decreases, therefore stress must increase. Increasing stress into a part that just got 4 additional holes added to it seems like a bad idea. I have become more cautious over time after being around a test lab in which you see what happens when parts fail. Sometimes small changes result in very unexpected failures. I have no interest in going down that road with my car.

^^^THANK YOU!

 

[Gun_Runner]

Absolutely true, but, it is a pretty safe bet that those cars do NOT have an extra set of holes drilled into the hub flanges, AND they are all converted to 5 lug hubs as well.

Group-B RS200
Shit was REAL back then too... cars that were putting out 900hp from a 1.8..... also, I'll try to find the billet rally hubs that you can buy for a Subaru. They were milled into a star shape to save weight.

 

[Goingnowherefast]

So there seems to be a lot of misinformation here so let me unpack this. Before I do that I will start and end by saying my advice to the OP is just get summer tires in 215/40/17 or the stock size and be done with it. . Next, we have to tackle the biggest fallacy here. The benefit of a wider tire is NOT more contact patch. The claim that wider tires have a bigger contact patch is incorrect. When you move to a wider tire, you make the contact patch wider, but you also reduce it's length. The way to increase contact patch is to lower the tire pressure, but that comes with several positives and negatives depending on different factors.

Regardless, there's three main reasons why a wider tire is generally faster than a narrow one for road course racing.

1. Heat Management. This is the greatest factor in why a wider tire will outperform a narrow one. A shorter, narrow tire will heat up faster, and blow past operational temp much faster than a wider, low sidewall tire. This is because heat dissipation is better with the wider (but not neccesarily greater contact patch) tire.

2. Sidewall stiffness. Due to how tires are constructed, a wide and short tire will have a much stiffer sidewall than a comparable tall and narrow one. This is because the stiff sidewall is necessary to support the wider tire. There's obviously huge benefits to sidewall stiffness for track racing, but the opposite goes for straight line racing.

3. Lateral slip factor. A wider tire will create more lateral force per slip angle which leads to better limit grip.

All three factors lead up to the conclusion that generally wider tires are better for road course racing.

Recap: If you're not doing track work, none of this matters. Just get some summer rubber and call it good.

 

[BRGT350]

After seeing an RS200 up close, those things are works of art. I couldn't take any pictures or share any details of the car, but can say those cars are insane.

 

[BRGT350]

Sorry if it seemed like I went aggro on you in that last post, but I get a lot of people that will tell me that my mod is dangerous, with no logical backing. This is then usually shortly followed by them installing big adapter spacers, which are ACTUALLY dangerous, and detrimental to performance and durability. I like to keep pictures of exploded adapter spacers, for those guys.


The other thing I wanted to address, that someone else brought up earlier, was knowing something you are modifying is causing stress to a safety component, and just accepting that as known risk.

This is a terrible idea that no one should do or accept. We all understand that putting a huge turbo on a 1.6 adds stress to the engine components, and you risk damage to the engine. This is fine, because new pistons can always be bought (and probably should have been before the big turbo, lol).
When you make a modification that takes away an aspect of safety, a modification that increases the car's safety by an equal amount should be made. For example, professional drag cars put tiny, light weight brakes on their cars for weight reduction and balance, but when they do this, they also install a parachute, as well as a roll cage. Get me? This is why I hate the "stanced" movement. It is dangerous, and detrimental to performance.

I quite often refuse to do bolt pattern conversions for guys, because they want a 4x112 pattern, and it only leaves 1.22mm of sidewall before the OD. I probably could have done 20 more of these conversions if I didn't care about other's safety.

no problem at all, no worries. I appreciate your insight and experience on the subject.

 

[M-Sport fan]

in terms of efficiency, a 8" wide wheel is the opposite direction you want to go. It is wider, most likely heavier, offers more aerodynamic drag, requires a wider tires which is also heavier and has more drag. Heavier wheels and tires require more torque (both acceleration and brake) to overcome inertia. Require additional damping due to the unsprung weight increase. I would go with a 7" wide wheel and a very aggressive tire compound. Take the money saved and go to a driver's school and find out that with better techniques, you won't be running out of traction with a 7" wide wheel and a 215mm (or even a 205mm) wide tire. On the street, you should never even come close to overcoming the traction of the stock ST. On the track, you should be working on practice and driver education and not lap times. Fast lap times are 90% driver and 10% car. Go for a ride in a production car with a professional driver and you will see what I mean. One of the most incredible rides in my life came from a car with 140ish horsepower, but with a professional driver. No tire size in the world could give me the amount of traction that is gained from a driver who understands exactly how to control a car.

^^^Could not be more correct and true whatsoever!

But, for street use purposes, and NOT for all-out performance purposes, I am going with the 17x8 1.2s with 215/40s on them, and I WILL 'admit' (as if I have to be guilty about it LOL) that it IS mostly for that 'tarmac rally' look mainly (like you did the Martini stripe livery theme on yours ).

I even would have gone with the OZed Superturismo LM/GT/WRC to get a more 'authentic' team look, IF they were available in an 8" wide for our cars, DESPITE their; cost, heft, and supposedly lower strength than even the 1.2s.

 

[Gun_Runner]

After seeing an RS200 up close, those things are works of art. I couldn't take any pictures or share any details of the car, but can say those cars are insane.

This is one billion percent truth. I know a guy that used to own one of the Street legal ones, and he said it was VERY rough around the edges though. Homologation car to the fullest.

Btw, regarding your question about chamfer/stress relief, yes I do chamfer all of the new holes. Sharp 90? are extremely prone to cracking.

 

[M-Sport fan]

Group-B RS200
Shit was REAL back then too... cars that were putting out 900hp from a 1.8..... also, I'll try to find the billet rally hubs that you can buy for a Subaru. They were milled into a star shape to save weight.

Yes, but I was speaking to the CURRENT WRC cars with the 5 bolt thing.

Besides, those cars in WRC spec did NOT make 900 HP, maybe up to 600/650.

Now, in 2.2 Evolution Rallycross configuration, yes, some may have been hitting close to the 900 mark.

 

[M-Sport fan]

After seeing an RS200 up close, those things are works of art. I couldn't take any pictures or share any details of the car, but can say those cars are insane.

Yup, 2 coil overs per corner, purpose designed and built frame, all-out BDT Cossie powerplant, etc., etc.

One of the coolest 'bits of kit' ever to come out of Ford's R&D in general (and I'm including the original, and development/evolutions of the GT40 in that), and Boreham in particular.

 

[BRGT350]

This is one billion percent truth. I know a guy that used to own one of the Street legal ones, and he said it was VERY rough around the edges though. Homologation car to the fullest.

Btw, regarding your question about chamfer/stress relief, yes I do chamfer all of the new holes. Sharp 90? are extremely prone to cracking.

this one was a street version, and yes, rough around the edges. It was 100% a rally car first and a road car a distant second.

 

[jeffreylyon]

We just stumbled onto a ton of anecdotal evidence. Mine is that I've re-drilled hubs on a couple of hard-driven RR cars with no problems and I've never heard of a failure on a re-drilled hub on the street or the track. We can collectively guess and speculate all we want, but that really gets us no where. The hub is ~ 3/8" of machined steel and the wheel is ~ 3/8" of cast aluminum - which do you think is going to fail first?

Also, I was mis-quoted as saying something along the lines that if you modify a safety component you're accepting that as a known risk. If that's what you read you where looking for it. Rhetorically, any modification to our cars that increases performance also increases stress except, perhaps, removing weight without compromising strength. Increasing stress increases the chance for a failure, whether that be an engine failure, a brake failure, or a hub failure (if you don't think that an engine is a safety item then you've never popped a hole in the sump at the end of a long straight). The more we chase performance the more we're going to have to "fix the weak link," or correct the failure. If you want to keep your car as "safe" as it came from the factory and the sack of lawyers and herd of reliability engineers that proofed it, don't touch it. If you want to modify it, the sky's the limit but, sooner or later, you're going to find the limit of something and it'll break, and there's not much that isn't a safety item when you're pushing the car (and yourself).

The only completely "safe" performance modification is to the dummy in the seat.

That being said, the 4x100 conversion is safe. Add stronger studs and longer lugs if that makes you feel better. Torque correctly and often and you're safer, in that regard, than 95% of the vehicles on the road.