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Downside to 305/30R20 on Rear Wheels

 
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Old 02-15-2019, 03:34 PM
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Default Downside to 305/30R20 on Rear Wheels

I'm currently at the EOL for my Pzeros and want to try MP4S tires for a change this go around per a lot of members reviews. I am now deciding between 295 or 305 on stock rear wheels.

I've perused through the various tire size forums but I am wondering if anyone has any feedback regarding unintended consequences of increasing the rear tire size to 305. I like the look of the wider tires but want to know if there are any pitfalls. I'm not horribly concerned with grip difference as that discussion has been beaten to death in previous threads.

Does anyone have a picture with 305/30R20 tires on stock setup with jag's 20" rear wheels? I am wondering if tires will bow out and look funny over rim or if they look like stock tires. I saw a picture of a tire on one of the tire threads on this forum that looked like it was crammed on the wheel and about to explode but not sure which size it was from the description - definitely don't want that.

Any issues with speed/handling of car with wider tires? I ran the question by my local Jag service rep, as he is a good guy and I trust his judgement, and it doesn't look like there are any warranty issues or mechanical risks so long as the tires are the same diameter. Wouldn't a 305 be slightly larger in diameter with the same AR?

Hoping someone with experience with both tires could chime in and give quick pros/cons of each. The wider tires look nice but want to be sure there are no unintended consequences of sizing up.
 
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Old 02-15-2019, 04:42 PM
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10mm is a very small amount. About this much rubber __ will be added to each side beyond the lip of the rim. No worries at all.

Go with the 305's and bury the go-fast pedal at all opportunities!
 
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Old 02-15-2019, 05:03 PM
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No experience with the tyres but there will be a slight increase in rolling diametre so speedo will read -slightly- different.
 
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Old 02-15-2019, 05:05 PM
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If 305/30/20 is the rear , what is the matching front size
 
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Old 02-15-2019, 07:22 PM
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Originally Posted by powerhouse View Post
If 305/30/20 is the rear , what is the matching front size
265/35-20. The 10mm upsizing will not look bulgy on the OEM wheels. The only downside is tire price.
 

Last edited by Unhingd; 02-15-2019 at 07:25 PM.
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Old 02-15-2019, 07:52 PM
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Typically a 10mm width increase would result in slightly more wheelspin. But the PS4S compound is so much better than the Pzero's you're running now, there really is no downside.
 
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Old 02-15-2019, 09:03 PM
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Originally Posted by Stohlen View Post
Typically a 10mm width increase would result in slightly more wheelspin.
And slightly more lateral traction.
 
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Old 02-15-2019, 09:42 PM
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And there are no warranty implications if something should go awry with the wheels, somehow, having the wrong size tire?

I've seen a few pics of 305s on stock 10.5" wheels and some look really bowed out, others not so much - maybe different aspect ratios or something. Really don't want to look like I'm riding on inner-tubes.

Anyone have any pictures by chance of MP4S or any other 305/30R20 tires on their stock wheels?
 
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Old 02-16-2019, 02:47 AM
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Hello, I drive 9x20 and 11.5x20 - 245/30 and 305/25.
But are not standard rims.

I also think that 10mm make no significant difference.

Visually, the mature could not look so pulled.
 
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Old 02-16-2019, 04:41 AM
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I have the 265 and 305's on stock wheels. Car is in garage for winter. Not sure what kind of photo I can get, but I'll give it a try. This set up will only be until April, when new 9.5 and 11 inch new two piece forged wheels are expected. The 10 mm extra is divided so it's only 5 mm per side.
 
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Old 02-16-2019, 02:16 PM
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Think standard 20" stock rims for the F-type seem to be 20x9 and 20x10.5 may be wider for svr, seems you can push to 265 for the front, but says 11.0 for 305, would it be safe to put the 305s on, seems ok from jaguny point of view
 

Last edited by powerhouse; 02-16-2019 at 02:28 PM.
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Old 02-16-2019, 07:15 PM
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A number of forum members have 305's on 11's. I am currently running them on 10.5's as are others. my dealer mounted the 265's and 305's on the oem wheels for me. Tire rack may have a chart showing 305's on 10.5 is acceptable.
 
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Old 02-16-2019, 09:04 PM
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The XKR-S GT has 305/30R20 on 10.5" rear wheels from the factory.

The XFR-S has 265/35R20 on 9" front wheels from the factory.

In other words, 10mm more is neither here nor there...
 
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Old 02-16-2019, 10:11 PM
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The charts for Michelin and pirelli on the tirerack site don’t quite lineup with powerhouse’s chart:
10.5” for 285-305
11.0” for 295-315
 
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Old 02-17-2019, 10:08 AM
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Wouldn’t the match for the 305/30/20 be the 265/35/20? The 305 has a 764 revolutions per mile and the 265/30 has 791. The 265/35 is 761 almost an exact match. I am specifically speaking about the AWD cars. I understand they are basically RWD until you need it but what about driving in snow/rain mode? Is it a basic esthetic thing?
The OEM’s match at 770 perfectly. I would never want to stress the AWD system having the front and rear working against each other fully understanding its not a direct link. But still.
 
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Old 02-17-2019, 10:31 AM
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Originally Posted by usgpru27 View Post
Wouldn’t the match for the 305/30/20 be the 265/35/20? The 305 has a 764 revolutions per mile and the 265/30 has 791. The 265/35 is 761 almost an exact match. I am specifically speaking about the AWD cars. I understand they are basically RWD until you need it but what about driving in snow/rain mode? Is it a basic esthetic thing?
The OEM’s match at 770 perfectly. I would never want to stress the AWD system having the front and rear working against each other fully understanding its not a direct link. But still.
Looks like OP has a RWD car, so he will have some flexibility on front size. Personally, for appearance sake I prefer 265/30/20 for the front over 265/35/20 which starts to sport too tall a sidewall IMHO. That issue aside for the moment, why is the OP stressing over this?

Given:
1) As most say there will be no traction improvement going to 305 (at least wrt to wheelspin)
2) Any size PS4S will be light years ahead of the stock P Zero
2) OP has stock wheels, 295's seem to sit perfectly on factory wheels
3) Price is higher for 305's
4) Esthetically, spacers and lowering springs would do more for the appearance of the car than upping tire size. And with increased tire size, there is less room for a proper spacer.

To me it's a no brainer, save $$ and stick with stock sizes...
 
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Old 02-17-2019, 11:15 AM
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Old 02-17-2019, 12:59 PM
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Originally Posted by Chawumba View Post
Looks like OP has a RWD car, so he will have some flexibility on front size. Personally, for appearance sake I prefer 265/30/20 for the front over 265/35/20 which starts to sport too tall a sidewall IMHO. That issue aside for the moment, why is the OP stressing over this?

Given:
1) As most say there will be no traction improvement going to 305 (at least wrt to wheelspin)
2) Any size PS4S will be light years ahead of the stock P Zero
2) OP has stock wheels, 295's seem to sit perfectly on factory wheels
3) Price is higher for 305's
4) Esthetically, spacers and lowering springs would do more for the appearance of the car than upping tire size. And with increased tire size, there is less room for a proper spacer.

To me it's a no brainer, save $$ and stick with stock sizes...
The price difference between 305 and 295 in minimal and well worth it for what I perceive to be a better/more muscular look from the rear of the car. To me, lowered cars with spacers do not look nice; those are not mods I myself would ever consider but I am very aware at how popular they are for other people - to each their own.

From just about everybody's experience, I do expect a better overall tire than the Pzero regardless of size I choose so it'll be a PS4S for me for sure. I'm thinking our RWD models may benefit from the improved compound even more than the AWD models.

I'm just trying to flesh out any negative impact a 305 tire might have. Primarily trying to figure out what a 305/30R20 looks like on stock rears. I have seen some wheel images that weren't clearly labeled in other threads and the tires look like are about to pop; the side walls bow out so much. Definitely want to avoid that, but as jaguny noted it's only 5mm on each side, not much at all really. I'm beginning to think the images I saw were of a completely different size tire.

I do have a RWD 14' so not too concerned about spin rate for front vs back, will probably keep front tires the stock size but may up size those as well.
 
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Old 02-17-2019, 01:16 PM
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Well, if it helps, here is a 295/30/20 on an 11" wheel... Note they were the old Pzero's, man I'm glad I sold those dogs.... On my car, switching to the PS4S's gave a tad more width at least visually.


 

Last edited by Chawumba; 02-17-2019 at 01:21 PM.
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Old 02-17-2019, 01:35 PM
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Default 305's on oem 10.5 wheel



 
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