Tire Upsize Guide


Thread Starter #1
Joined
Mar 28, 2011
Messages
2,865
Likes
2,138
Location
Madras
A simple guide and a piece of material to go through before you think about Tire upsizing.

Why?
- Upsizing improves aesthetic looks
- To enhance performance (better grip / traction, etc)

Types
Upsizing normally involves increasing any/few/all of the below parameters
- Section Width
- Aspect Ratio / Aspect height / Sidewall thickness
- Rim diameter
Listing out few common upsize options (only a few were listed here, apart from this we have many other options aswell)
Tire.jpg

Impact / Effects
Tire upsize has both Pros and Cons same as other performance modifications.

Positive Impacts
Aesthetics
Larger tires give a hot look to the vehicle. Better presence inside the wheel arch could be felt.
diff size.jpg
15"~19~ wheels on a VW Golf (Image Source: Google)

Road Grip
Increased section width increases the tire contact area with the road. This results in better road grip, better traction. Better grip translates to better braking and steering control.

Negative Impacts
Fuel Economy
Upsizing the tire will result increase in overall mass. Added mass is always considered as enemy to fuel economy.

Layout
OEMs design the layout of all the moving parts considering a certain level of tolerance and there will be a little margin for the customer to go beyond the design spec. But we aren't sure about the so called "margin". When the upsize is beyond the margin, tire / wheel will interfere with the surrounding parts (wheel arch, body, suspension parts, drive shaft, etc) during extreme steering angle and suspension stroke.

Ride & Handling
Larger side wall thickness --> Less stiffness
Thinner sidewalls --> High stiffness

With a larger rim dia and maintaining the overall diameter / circumference of the tire, we sacrifice the side wall thickness. This will stiffen our ride. Higher the stiffness, deteriorated ride characteristics. On the other hand, stiffer tire improves handling.

Taking an example of upsizing with larger sidewall thickness, Ride will be improved compromising the Handling characteristics.

Acceleration & Speed
Larger the overall diameter / circumference, less the acceleration. For city driving acceleration is most important, infact rate of fuel consumed during acceleration is larger than that of cruising. For highway run (cruising mode) increase in diameter will contribute a increased top speed and fuel economy aswell (on the positive side) To be crisp, fuel economy gets affected with change in overall diameter.

Note: We get speedo error when the overall diameter / circumference is affected.

Gradeability
Gradeability or hill climbing is proportional to acceleration performance. Increase in overall diameter affects the vehicle gradeability performance (may not be on a larger extent, but certainly there will be an impact) Frequent down shifting or prolonged driving in lower gears will be required when the tire is upsized.

Impact to other parts
- Larger the overall diameter, higher the torque / load on the drive shafts
- Larger the overall diameter, higher the braking force required (or a brake upgrade required)
- Stiffer the tires, more shock transfer to the body (via suspension)
- Wider the Tires, higher the steering effort
 
Last edited:

Akash1886

Honoured Member
Joined
Sep 7, 2014
Messages
10,511
Likes
13,014
Location
Delhi-NCR/ Mumbai
I was advised to up-size the Tyre of my City I-vtec to 195 Sections as at present its 175/55 R15. But after reading this, I feel positives of up-sizing are way too less than negatives. Hence, Idea forever dropped.

Thanks Satish for this wonderful info!

Regards

Akash
 
Last edited:

Akash1886

Honoured Member
Joined
Sep 7, 2014
Messages
10,511
Likes
13,014
Location
Delhi-NCR/ Mumbai
Section width increase without affecting the overall diameter is not that bad. You can go ahead.
Satish, its better to let Tyre remain stock. What if some issue crops up after up-sizing! You have seen how involved I have been with my car. But, I can't dare to take a chance on this now buddy.

Regards

Akash
 
Joined
Oct 15, 2011
Messages
4,244
Likes
3,366
Location
Some Village
Mr Boss,
My hyundai i10 currently runs stock 155/80 R13 and simply feel inadequate.
Whats the maximum safe upgrade on stock rims?
 
Joined
Feb 17, 2013
Messages
603
Likes
433
Location
Kannur, Payangadi
Mr Boss,
My hyundai i10 currently runs stock 155/80 R13 and simply feel inadequate.
Whats the maximum safe upgrade on stock rims?
175/70R13 is the safe bet, you get many choices aswell.

Whats the width of i10's stock rim? AFAIK its 4J.[confused]

As Mr.Boss said 175/70/13 is the best upgrade. If and only if your stock rim width is more than or equal to 4.5J

I had 155/80 R13 in my A-star. Luckily it had 4.5J rim, so upgraded to 175/70 R13 XM2.

Regards.,
 
Joined
Oct 15, 2011
Messages
4,244
Likes
3,366
Location
Some Village
Whats the width of i10's stock rim? AFAIK its 4J.[confused]

As Mr.Boss said 175/70/13 is the best upgrade. If and only if your stock rim width is more than or equal to 4.5J

I had 155/80 R13 in my A-star. Luckily it had 4.5J rim, so upgraded to 175/70 R13 XM2.

Regards.,
The rim is actually 4.0B
Now whats the difference in 4J and 4.0B rims?[confused]
 
Joined
Oct 15, 2011
Messages
4,244
Likes
3,366
Location
Some Village
Waiting for the experts to comment.[roll]
From where did your read 4.0B, User Manual? Have you checked whats written on your rim?
I found it on online discussions. about the user manual I'll check today. btw where to check on rim? there's nothing written on face.
 
Joined
Oct 15, 2011
Messages
4,244
Likes
3,366
Location
Some Village
found a good readout-
J, JJ, K, JK, B, P and D : Tyre bead
profiles / rim contour designations.
No, my keyboard letters weren't stuck down
when I typed this. The letter that typically
sits between the rim width and diameter
figures stamped on the wheel, and indicates
the physical shape of the wheel where the
tyre bead meets it. In the cross-section on
the left you can see the area highlighted in
red.
Like so many topics, the answer as to which
letter represents which profile is a long and
complicated one. Common wisdom has it
that the letter represents the shape. ie. "J"
means the bead profile is the shape of the
letter "J". Not so, although "J" is the most
common profile identifier. 4x4 vehicles often
have "JJ" wheels. Jaguar vehicles
(especially older ones) have "K" profile
wheels. Some of the very old VW Beetles
had "P" and "B" profile wheels.
Anyway the reason it is an "awkward topic
to find definitive data on" is very apparent if
you've ever looked at Standards Manual of
the European Tyre and Rim Technical
Organisation. It is extremely hard to follow!
There are pages and pages (64 in total) on
wheel contours and bead profiles alone,
including dimensions for every type of wheel
you can think of (and many you can't) with
at least a dozen tabled dimensions for each.
Casually looking through the manual is
enough to send you to sleep. Looking at it
with some concentration is enough to make
your brain run out of your ears. To try to
boil it all down for you, it seems that they
divide up the rim into different sections and
have various codes to describe the geometry
of each area. For example, the "J" code
makes up the "Rim Contour" and specifies
rim contour dimensions in a single category
of rims called "Code 10 to 26 on 5deg.
Drop-Centre Rims". To give you some idea
of just how complex / anal this process is,
I've recreated one such diagram with
Photoshop here to try to put you off the
scent.
From the tables present in this manual, the
difference in dimensions between "J" and
"B" rims is mainly due to the shape of the
rim flange. This is the part in the diagram
defined by the R radius and B and P min
parameters. Hence my somewhat simpler
description : tyre bead profiles.
Note that in my example, the difference
between "J" and "B" rims is small but not
negligible. This area of rim-to-tyre interface
is very critical. Very small changes in a
tyre's bead profile make large differences in
mounting pressures and rim slip.
"A" and "D" contour designations come
under the category of "Cycles, Motorcycles,
and Scooters" but also show up in the
"Industrial Vehicles and Lift Trucks"
category. Naturally, the contours have
completely different geometry for the same
designation in two different categories.
The "S", "T", "V" and "W" contour
designation codes fall into the "Commercial
Vehicles, Flat Base Rims" category. The "E",
"F", "G" and "H" codes fall into the
"Commercial Vehicles, Semi-Drop Centre
Rims" category. Are you beginning to see
just how complex this all is?
I think the best thing for you, dear reader, is
a general rule-of-thumb, and it is this : if
your wheels are stamped 5 J 15 and you buy
5 K 15 tyres, rest assured they absolutely
won't fit.

Car Bibles : The Wheel and Tyre Bible Page 4 of 4
Rims: B vs J - Automotive tire/wheel engineering - Eng-Tips

so... the B or J sizes are not revalent to width. i10 has simply 4 inch rims.
 
Joined
Apr 26, 2012
Messages
1,253
Likes
394
Location
cochin
Mr Boss,
My hyundai i10 currently runs stock 155/80 R13 and simply feel inadequate.
Whats the maximum safe upgrade on stock rims?
Most of the New cars coming with 14' wheels and above only. Tire companies are reducing the production of broader tires below that. There may be shortage of broader tires in 13' in coming years. In case you are going for broader tires, it is better to select 14' alloys and tires.

In 13' - go for 175/70-13 ( in case only of stock wheels)
In 14' - go for 175/65-14 ( If buying alloy)

There will not be much difference in tire price with these 2 varients. On the other side, your stock size tire will be rs.800-1000 cheaper compared to these models and also give better milage and lasting. I have good experiance on 3 varients mentioned above.
 
Last edited:
Top Bottom