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The standard ST tire has a 245 mm width, the much more powerful RS is going with a 235. Anyone heard an explanation from Ford as to why? Certainly runs counter to the usual practice. To make it easier to drift?
 

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The standard ST tire has a 245 mm width, the much more powerful RS is going with a 235. Anyone heard an explanation from Ford as to why? Certainly runs counter to the usual practice. To make it easier to drift?
You want the narrowest tire possible that still offers the performance you want. Wide tires are more likely to hydroplane, track along defects in the broad, have higher rolling resistence, have poorer snow traction and are more expensive. The ST is just FWD and needs wider tire size to provide grip where as the RS' AWD spreads the tractive effort out to all the tires.
 

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Could be an interference condition. No scrape scrape like lowered cars
 

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2015 st's come with 235/40/18's
RS with come with 235/35/19's

your math appears flawed.
This.
My guess is 235 is the widest they can fit in those wheel wells without rubbing while keeping a mild camber setting that provided an even "normal" tire wear. Wish it came with 245s like the STI, though. I also had 245s on my WRX and with the right strut valving, it was comfortable on the street... And roads here are brutal.
 

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I bet 255's would fit without much fuss.
a 255/35 will only be 2.12% slower and .5" taller
What kind of camber/wheel offset would you need to run without rubbing on 255s? I have no experience with the focus chassis so I'm clueless here
 

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in a mac strut car the usual issue is the inside of the tire rubs on the strut at full lock
I think the differences between the front track on the st and rs will make it hard to use the st as a benchmark for what will work on the rs. the track of the rs is .3" wider in the front and .4" wider in the rear.
here is a 255 on a ST with the stock rims (8")
enu9yhed.jpg

its possible we will have less room than the st, but until we have the car, its purely a guess, but I imagine 255's will be the widest we can go without getting exotic.
 

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in a mac strut car the usual issue is the inside of the tire rubs on the strut at full lock
I think the differences between the front track on the st and rs will make it hard to use the st as a benchmark for what will work on the rs. the track of the rs is .3" wider in the front and .4" wider in the rear.
here is a 255 on a ST with the stock rims (8")
View attachment 2669

its possible we will have less room than the st, but until we have the car, its purely a guess, but I imagine 255's will be the widest we can go without getting exotic.
thanks for the comparison. I forgot about the wider track. It really is a wait-and-see situation.

That tire bulge on an 8" wheel is too much for my taste. Tire flex on cornering might be too much unless the sidewall is super stiff? I know it's doable, but most tire manufacturers put a 9" wide wheel at the sweet spot of a 255's allowable wheel width range and 8.5" is usually the minimum. I did like how my 245's looked and felt on a 8.5" wheel... Perfectly squared. Personal preference I guess.
 

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@Devon K

235/35/19 explained....

If your concern is tire width and grip, the RS has 4 powered tires with a total width of 940mm. The ST, whether the tires are 235 or 245 have 2 powered tires for a total width of 470-490mm.

If comfort is your concern, the sidewall height can be calculated... RS = 235/35 tires that have an 82mm (235 x 0.35) sidewall height. The ST would have 94mm (235 x 0.4) sidewalls. That may provided a little bit more comfort but is is only 12mm different.

The drivetrain obviously doesn't provide an even 25% of power to each tire, so it's not as simple as I've stated above, but still, the RS will have plenty of grip and Ford has chosen these tires for a reason.
 

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@Devon K

235/35/19 explained....

If your concern is tire width and grip, the RS has 4 powered tires with a total width of 940mm. The ST, whether the tires are 235 or 245 have 2 powered tires for a total width of 470-490mm.

If comfort is your concern, the sidewall height can be calculated... RS = 235/35 tires that have an 82mm (235 x 0.35) sidewall height. The ST would have 94mm (235 x 0.4) sidewalls. That may provided a little bit more comfort but is is only 12mm different.

The drivetrain obviously doesn't provide an even 25% of power to each tire, so it's not as simple as I've stated above, but still, the RS will have plenty of grip and Ford has chosen these tires for a reason.

You are also only addressing one segment of the traction circle in terms of use.

I bet a stock RS would be faster on track with 245s of the same compound due to the slight increase in corner entrance and exit speeds, most straights will likely end at the same MPH (rolling resistance and more weight makes it harder to accelerate that 245, if marginal). 255 might be too.. or might be a little slower. Only testing will say for sure.

The sidewall difference is required by the decision to run 19s vs 18s but wanting the same overall diameter. I'll run 235/40/18s on the street wheels and play with the forged/track wheels over time.
 

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Discussion Starter #12
@Devon K

235/35/19 explained....

If your concern is tire width and grip, the RS has 4 powered tires with a total width of 940mm. The ST, whether the tires are 235 or 245 have 2 powered tires for a total width of 470-490mm.

If comfort is your concern, the sidewall height can be calculated... RS = 235/35 tires that have an 82mm (235 x 0.35) sidewall height. The ST would have 94mm (235 x 0.4) sidewalls. That may provided a little bit more comfort but is is only 12mm different.

The drivetrain obviously doesn't provide an even 25% of power to each tire, so it's not as simple as I've stated above, but still, the RS will have plenty of grip and Ford has chosen these tires for a reason.
When the RS puts 70% of its torque to one rear wheel it will just about matching in its power output to that one wheel the power that the ST could put to one of its front wheels if its brake torque vectoring redirected all the engine's torque to one wheel. The former scenario seems a more likely occurrence in spirited driving than the latter, which would presumably only happen if one of the ST's wheels had no traction at all (ice, extreme mass transfer). So the argument could be made that wider rubber could still enhance the RS's grip relative to the ST - and the RS is after all designed to be in a higher performance class than the ST.

Ford may have run into body design limitations there - they didn't flare the fenders on this generation of RS so perhaps they did not like the clearances they got with 245s, and chose to increase the performance differential another way, by getting the custom Michelin Pilots made for the car.

Even if the RS's performance doesn't take a hit from the 235 rubber, wider boots would have given the car a more aggressive and planted look, and done more to offset its tall height (it's 4" taller than the Mustang after all).
 

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I would say cost, feel and efficiency were the main reasons they stuck with a 235 tire. I have a set of Team Dynamics that are 18x9's +38 offset and wrap them with 245 rubber. no rubbing issues lock to to lock, but even with 245s the car does rub under hard cornering and over big bumps. That's partly due to the steeda springs.
 

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2015 st's come with 235/40/18's
RS will come with 235/35/19's

your math appears flawed.
^what he said...

All Focus STs come stock with 235s. 235's are probably the only thing that will fit. They already had to reduce the maximum steering angle (aka give it a huge turning radius) to get the 235s to work.

PS: The turning radius on the ST is larger than the Ford Explorer.
 

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Discussion Starter #17
^what he said...

All Focus STs come stock with 235s. 235's are probably the only thing that will fit. They already had to reduce the maximum steering angle (aka give it a huge turning radius) to get the 235s to work.

PS: The turning radius on the ST is larger than the Ford Explorer.
Yeah, I used an incorrect source on the ST - a car rag reviewer was wrong. Still the fact that Ford didn't go wider than the ST is interesting - and that bit about the turning radius makes it clear why: at 39.4 feet for the ST, that's already a few feet larger than a Mustang or Corvette.
 

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Discussion Starter #18 (Edited)
Just came cross this Google translation of a German review in the "all in one first impressions" thread:

Inside it is quite comfortable and to both the fuel consumption and the turning circle has been reduced. Expressed in figures: A RS-driver has now 7.7 liters Super per 100 kilometers according to refill. At the same time to make it to at least one turn less out of a tight parking spot."
So it's possible that changes in the RS's steering setup relative to the ST has reduced its turning circle - great news if true.

EDIT: Here's what Autoblog has for the RS turning radius: "Turning radius 18.7" LOL. Must have been driving an RC version.
 

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I really hope we can fit something wider. Even my current "narrow" snow tires are 255.
 
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