FD Wheel and Tire Sizing
#101
Call me gramps!
I'm going to need traction, and I'm going to need it bad.
What would be the optimal offset/wheel width if I plan on running 18" diameter and 315mm width in the rear? How about the front? And I do plan on rolling the fenders. Thanks in advance.
What would be the optimal offset/wheel width if I plan on running 18" diameter and 315mm width in the rear? How about the front? And I do plan on rolling the fenders. Thanks in advance.
#103
Rob
iTrader: (2)
You won't be able to fit 315's in the rear without ridiculous camber and modifications to the sway bar mounts and inner fenders. Even with my rear flares it's a tight fit. I think a 285 (though a 295 might squeeze in by a hair margin) is about is wide as you can go in stock wheel wells before you start running into clearance issues.
#104
Limitations, exceptions and loopholes.
This is my first post here, so don't take this as me being a d*^& and pissing all over something that is in fact cool. However, I have lived and breathed wheel and tire fits for a living.
There are two critical effects of tire sizing being left out by Jimlab's original spreadsheet. One is overall tire diameter, the other is the actual width of the tire, installed on the wheel.
If a tire has a shorter overall diameter, it will have more clearance to the fender at all points. For example, a 245/40-17 will have approximately 0.5-in more clearance to the fender in all directions than a 245/45-17 (looking at mfr. tire data more than calculations based on nominal). The same thing can apply to variations from nominal. Hoosier has historically cheated the OD of certain tires downward. For example, a 275/40-17 typically measured 25.3 or 25.4 OD, whereas the nominal works out to 25.7ish. This let those tires go places that others of the same nominal size would have had problems.
The inner and outer clearances are all based on wheel width. As far as I can tell, the spreadsheet assumes that the sidewall of the tire will be 1/2-in. out from the bead seat all the way up to the tread. Discussion in this thread says that is assumed to be the plane of the outer face of the wheel. As I played with the numbers, changing tire width had no effect on clearance. I have a set of 18x10.5 wheels. The spreadsheet points to a 295 width, but I would more likely use a 285/30 or 265/35. These would give me more clearance, but the spreadsheet doesn't show it.
There are also variations from nominal in width. According to data sheets, in 265/35-18, the BFG R1 and Yoko Neova both measure 10.7-in. in section width on a 9.5-in. wheel, while the Michelin PS Cup measures 10.9-in. The 255/40-17 PSC is almost as wide as a 275/40-17 Hoosier. Some tires also have more rounded profiles, some have more square shoulders. Also, as a rule of thumb, the actual section width of a tire increases approximately 0.2-in. for every 1/2-in. increase in wheel width. (I didn't make that up, I just got it from a Michelin motorsports engineer.) That lets you work your way from measuring rim width on tire data sheets to whatever wheel you are planning. All these details matter.
Random detail worth mentioning: I've never found a 265/30-18 tire. I have found evidence that there was once a 265/35-17 Yokohama of some sort, but if so, it has been out of production so long I can't verify it.
I haven't invested to understand the QE3K sheet as thoroughly.
For sure, this is a good tool, but ultimately, if you're pushing the envelope, you'll have to either follow exactly what someone else did, or understand that you may spend some money on "research".
Still, this has helped me understand the FD fit a lot better, so thanks!
There are two critical effects of tire sizing being left out by Jimlab's original spreadsheet. One is overall tire diameter, the other is the actual width of the tire, installed on the wheel.
If a tire has a shorter overall diameter, it will have more clearance to the fender at all points. For example, a 245/40-17 will have approximately 0.5-in more clearance to the fender in all directions than a 245/45-17 (looking at mfr. tire data more than calculations based on nominal). The same thing can apply to variations from nominal. Hoosier has historically cheated the OD of certain tires downward. For example, a 275/40-17 typically measured 25.3 or 25.4 OD, whereas the nominal works out to 25.7ish. This let those tires go places that others of the same nominal size would have had problems.
The inner and outer clearances are all based on wheel width. As far as I can tell, the spreadsheet assumes that the sidewall of the tire will be 1/2-in. out from the bead seat all the way up to the tread. Discussion in this thread says that is assumed to be the plane of the outer face of the wheel. As I played with the numbers, changing tire width had no effect on clearance. I have a set of 18x10.5 wheels. The spreadsheet points to a 295 width, but I would more likely use a 285/30 or 265/35. These would give me more clearance, but the spreadsheet doesn't show it.
There are also variations from nominal in width. According to data sheets, in 265/35-18, the BFG R1 and Yoko Neova both measure 10.7-in. in section width on a 9.5-in. wheel, while the Michelin PS Cup measures 10.9-in. The 255/40-17 PSC is almost as wide as a 275/40-17 Hoosier. Some tires also have more rounded profiles, some have more square shoulders. Also, as a rule of thumb, the actual section width of a tire increases approximately 0.2-in. for every 1/2-in. increase in wheel width. (I didn't make that up, I just got it from a Michelin motorsports engineer.) That lets you work your way from measuring rim width on tire data sheets to whatever wheel you are planning. All these details matter.
Random detail worth mentioning: I've never found a 265/30-18 tire. I have found evidence that there was once a 265/35-17 Yokohama of some sort, but if so, it has been out of production so long I can't verify it.
I haven't invested to understand the QE3K sheet as thoroughly.
For sure, this is a good tool, but ultimately, if you're pushing the envelope, you'll have to either follow exactly what someone else did, or understand that you may spend some money on "research".
Still, this has helped me understand the FD fit a lot better, so thanks!
#105
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Hi Guys! I'm running on stock 16'' wheels and i need to change my tyres. Currently, the size is 225/50/16. How much wide can i go with the same wheel size? I read all the thread but it seems that i'm getting nowhere (stupid me). Can anyone help please? (P.s The car has been lowered but unfortunately i do not know by how much, as i bought the car already like this from Japan) I've also included a couple of pics of the car with the current tyres (if it helps). Thanks!
#108
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I don't have many good pics, but these might work. The RA-1 is used a lot in vintage racing on 914/6 porsche and such. excellent track day tire too, even in the rain. they are pretty cheap, so even if the car is driven on the street they could be replaced fairly often if need be- Not sure of what kind of street driven tread life you would get, but this is the only tire I'll use on stock wheels on this car. Toyo has a new dot legal race tire, but I don't think they have 245-45-16 size yet.
t
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#111
Super Snuggles
Thread Starter
the other is the actual width of the tire, installed on the wheel.
It's a matter of personal preference, and since the width of the wheel does not vary, the width of wheel is used for clearance calculations. After all, it is wheel that will come into contact with suspension components, and not the tire. Fender lips and liners are another story, and that's why a 1/2" margin of clearance is advised beyond the edges of the wheel.
If a tire has a shorter overall diameter, it will have more clearance to the fender at all points.
The inner and outer clearances are all based on wheel width. As far as I can tell, the spreadsheet assumes that the sidewall of the tire will be 1/2-in. out from the bead seat all the way up to the tread.
I have a set of 18x10.5 wheels. The spreadsheet points to a 295 width, but I would more likely use a 285/30 or 265/35. These would give me more clearance, but the spreadsheet doesn't show it.
#112
Rob
iTrader: (2)
Fender lips and liners are another story, and that's why a 1/2" margin of clearance is advised beyond the edges of the wheel.
#113
Super Snuggles
Thread Starter
I also added the a 1/2 inch to the other sheet because every rim that I have measured in person is actually 1 inch wider than the advertised bead width. It is pretty much standard for the rim lip to extend about 1/2" beyond the inner edge which retains the bead on each side.
#115
Corn Fed FD
iTrader: (1)
this is a long thread and it is my first visit but i thought it might be worthwhile to share my setup.
my background is roadracing and my FD is getting close to being complete for dual street and road racing usage.
we all have differing objectives w our FDs. having raced for 22 seasons and hung up spending my entire spare time at the track i am not interested in doing a track only car.... cage, fuel cell, trailer etc. i want a car that i can do a few track days and lay down some fast laps but also enjoy just cruising.
suspensions and tires were always number one on my agenda when i was racing. i was sponsored by Hoosier and they would make tires for me for each of my races. i would spend most of my time looking at them after sessions. i also used softeners on them. i slept w them.
anyway i have finalised my 08 tire sizing. my car runs very close to 54% rear weight. i run 18 X 9.5 fronts and 18 X 10.5 rears which i consider to be the optimum sizing for my application. front offset is 40, rear 30. i run small rear fender flares as i needed about 5/8 of an inch w my Toyo 285s. i run 25 inch ride height front and rear.
i will run sizing that will deliver tread width equal to my wheel width: 265 front and 295 rears.
the operative concept for me, since tires are number one in my book, was that i would not base my sizing on the body but on performance.
i will be running a UTQG around 140-160 and may shave a few tires.
i will also be running the 08 Silver State Classic in Sep.
here's a pic of my flares... i did the work and am happy w the result. final paint still awaits.
hc
my background is roadracing and my FD is getting close to being complete for dual street and road racing usage.
we all have differing objectives w our FDs. having raced for 22 seasons and hung up spending my entire spare time at the track i am not interested in doing a track only car.... cage, fuel cell, trailer etc. i want a car that i can do a few track days and lay down some fast laps but also enjoy just cruising.
suspensions and tires were always number one on my agenda when i was racing. i was sponsored by Hoosier and they would make tires for me for each of my races. i would spend most of my time looking at them after sessions. i also used softeners on them. i slept w them.
anyway i have finalised my 08 tire sizing. my car runs very close to 54% rear weight. i run 18 X 9.5 fronts and 18 X 10.5 rears which i consider to be the optimum sizing for my application. front offset is 40, rear 30. i run small rear fender flares as i needed about 5/8 of an inch w my Toyo 285s. i run 25 inch ride height front and rear.
i will run sizing that will deliver tread width equal to my wheel width: 265 front and 295 rears.
the operative concept for me, since tires are number one in my book, was that i would not base my sizing on the body but on performance.
i will be running a UTQG around 140-160 and may shave a few tires.
i will also be running the 08 Silver State Classic in Sep.
here's a pic of my flares... i did the work and am happy w the result. final paint still awaits.
hc
they look great,
I wana get 10.5, 18s with 15offset
I wonder if similar flares will cover them
#116
Non Runner
iTrader: (3)
I'm not sure what offsets I will need with my new bodywork. I'm thinking this:
Front:18x9.5 with 255/35 tires.
Rear:18x10/10.5 with 285-295/35 tires.
My arches are flared by:
Front: 2.5cm extra
Rear 2cm extra.
Any idea what kind of offsets would be right for this application?
Cheers.
Front:18x9.5 with 255/35 tires.
Rear:18x10/10.5 with 285-295/35 tires.
My arches are flared by:
Front: 2.5cm extra
Rear 2cm extra.
Any idea what kind of offsets would be right for this application?
Cheers.
#117
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#123
Rotary Freak
I'm looking at 2 sets of wheels.
Option one is for track racing:
10X18 all around with offset 45: 255/35/18 tires on 4 corners
Option 2 (show wheels)
8.5X19 front offset 42
9.5X19 rear offset 43
tire size whatever is needed
What I find weird is that I see some people running 10X18's on 4 corners with offset 50 on all of the wheels (with coilovers) and the spread sheet tells me otherwise (possibly because of the coilovers)
Are the above offsets possible with stock FD body or lightly rolled fenders?
Option one is for track racing:
10X18 all around with offset 45: 255/35/18 tires on 4 corners
Option 2 (show wheels)
8.5X19 front offset 42
9.5X19 rear offset 43
tire size whatever is needed
What I find weird is that I see some people running 10X18's on 4 corners with offset 50 on all of the wheels (with coilovers) and the spread sheet tells me otherwise (possibly because of the coilovers)
Are the above offsets possible with stock FD body or lightly rolled fenders?