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-   -   Maruti 800 : Tyre & wheel upgrade thread (https://www.team-bhp.com/forum/tyre-alloy-wheel-section/11549-maruti-800-tyre-wheel-upgrade-thread.html)

Dear friends,
Yesterday I took the expressway to Mumbai from Pune as usual.
Was driving my 29,000 km Maruti 800 5-speed MPFI.

After the Deole overpass, I heard a funny sound, like a periodic metallic ringing.
Pulled over onto the hard-shoulder to investigate. The air in all 4-Goodyear 145/70R12s looked OK and the tire-carcasses weren’t warm to the touch either.
Got back into the car and drove another kilometer. The periodic metallic ringing grew louder.

Luckily the expressway exit for Lonavala came up. I got off the expressway and pulled into the Hotel Center-Point where all the Mumbai-bound Neeta Volvos stop for tea.

On the surface of my left rear tire a four-inch long strip had delaminated and the steel-belts of the radial were showing. The four-inch long strip was hitting the wheel arch at speed.

Changed the wheel and proceeded to Chembur, Mumbai.



In the evening, I changed all five tires to MRF ZVTS 145/80R12. The rolling diameter and ride height has now slightly increased [1.45 cm] and the ride is discernibly softer (lower noise, vibration & harshness).

I realize that the 145/80R12 are meant for the Zen VXi and Alto.


Does anybody think that the tire-upsize is technically wrong?

There is a difference of 5.7% in circumference b/w both tyres..Max recommended difference is 2-3%.....U will now face speedo errors....

Good choice....Amazing grip for that small size tyre n minimal tyre wear....

Yes it is wrong!...
the total circumference has increased by 30mm i.e. 3cm.
The issues could be...
1) A 6% error in the speedo
2) Tyre might touch the inside while the car is fully loaded or steering fully turned.
3) How did you manage to squeeze the spare tyre in to the much smaller space?

My cousin had put 165/70 R12 on his 800..... again the same alto, zen size... his tyres ceratinly did scrape the insides under full load.

Also depends on what rim size your cousin running with....
Dont think 145/80 12 will scrape anyhow....

He was running on stock rims...
But again I believe his problem was more due to the width of the tyre.

You can try following tyre size calculator
http://www.miata.net/garage/tirecalcold.html

Friends, the old radial tires were of type: Goodyear 145/70R12-69S.

Some research revealed that:

The first number: 145 is the tire’s section width in millimeters from sidewall to sidewall, under no load.

The second number 70 is the aspect ratio. The ratio of the section height (height of the tire sidewall), expressed as a percentage of the width. In this case, 70% of 145mm is 101.5mm - the section height.

The third number 12 is the metal wheel rim diameter (in inches) that the tire is meant for. Why do they mix inches and millimeters? Beats me! Couldn’t they have kept the spec. all metric and simply called it a 145/70R305?

The last number 69 is a load capacity index. It refers to the load carrying capacity of the tire at maximum air pressure. A 69 rated tire is good for 325 kg load on each wheel.

The "S" means that the tire is good for speeds upto 112 mph [180 km/hr]

Anyway, the choices with me for new radials for the Maruti 800 were
145/70R12 (the original size), 155/70R12 and 145/80R12.



Tire width translates to the area of contact with the road, influencing rolling friction and therefore fuel economy. I thought of upgrading to bigger rubber, for better comfort, without compromising the section width.

So I purchased a set of 5 MRF ZVTS 145/80R12-74S radials, from Guardex Tyres, Chembur, Mumbai. They are an MRF tyres & service outlet.
The new tires set me back by Rs. 7,875/=

The 74 rated tires are good for 375 kg load on each wheel.
I also had the wheels dynamically balanced and the suspension geometry angles realigned.

Positives:
The car now drives like a dream. The ride quality, absorption of noise, vibration and harshness is decidedly superior.
The rough and patchy roads of Pune, are less likely to ding and dent the wheel rims. I plan to change to 12" alloys next.
The ground clearance has gone up by 1.45 cm.
And the overall gearing is now 5.7% taller, so there will be better fuel economy.

And importantly, the bigger wheels don’t interfere with the wheel-wells, neither while steering nor while bouncing over a speed-bump. An initial concern which turned out to be a non-issue.


Negatives:
The overall diameter has increased from 507.8 mm to 536.8 mm. This means that the speedometer and odometer indicate readings 5.7% less than actual. When the speedo indicates 100 km/hr, the car is actually doing 105.7 km/hr.
The spare wheel is now slightly larger than the space available in the recess in the luggage compartment. I plan to tweak the welded steel strip that holds the wheel down, to accommodate the new wheelsize.

I wonder .. if it was so simple to put a BIGGER tyre why don't manufacturers do it?
Better fuel economy?.. due to change in gear ratio?... theoritically yes. Then why don't manuacturers do it?
Better ride? ... yes..
better handling? .. yes (provided it was on 13" rims)

Then whats the down side? nothing?
No, there has to be something! maybe I can't think of it!
For one, increasing ride height is NOT good for handling.

Can someone tell me the downside?

hey man my 800 is the 96 model i have changed 3 tyres all my originals were dunlops!damn those tyres have reaally lasted my car has not even touched 35k km still on 34k well now i have 3 new jk tyres a few days back the front tyre punctured due to a nail so when i removed it to change it with the stepnee i was amazed the whole inner side of the tyre thread was almost worn off now i understand why my car used to pull to the left!well i wanted to know were the original tyres radials???and why are the 800 tyres so bloody thin??

96 model.... no radials... it was Bias ply back then.
Try a set of radials... if not already running on them.. you'll feel the difference instantally.

thanks slk im already running on all radials now!

Sounds like your suspension geometry could use some work.

Have a good Maruti workshop return everything back to original spec.
Get your front wheels aligned regularly. This is especially important, after a fast and nasty bump on the unexpected speed-breaker or any front-end collision (even a minor one).

Maruti 800s are notoriously frail and delicate.

I'm unsure!
AFAIK, a 1996 Maruti 800 came original with bias-belted cross-ply tires 4.50-12s, I think.

When Maruti Udyog finalized on Suzuki's 800 model in 1982, the whole world was already using radials. In fact, Michelin of France first introduced steel-belted radial tires as far back as 1948.

Maruti, India was one of the rare manufacturers that took a modern car designed for radials and retro-fitted it with bias-ply tires. Of course, bias-ply tires were cheaper and could be retreaded after wearing out.

By thin tires, I presume you mean narrow tires.
Well, if so, the only argument for narrow tires is fuel economy.
The wider the tire, the better the road grip, and the more the frictional rolling resistance.
The 800's dimunitive 796cc 3-cylinder engine (particularly the carburetted one) can only push so much rubber, economically.

I like the idea of ram's decision. I would like to go this tyre (145/80R/12). I guess negative is not only with the speedometer and odometer I think it has got some effect on the wheel axle too. The axle of the car will be designed for that particular rim size and trye size. If we are going in for a bigger tyres It might put more weight on the axle as well, as Ram says if we go for the 12" alloy wheel and the bigger tyre ratio then it might compensate the weight and definately be on the pro side.
Thanks ram I will keep this in my mind when I go for a change of tyres for my 800 :-) *peace*

Axle designs of cars are always over-designed to tolerate three to four times the axle load. This is called factor-of-safety. Typically in the Maruti 800 this is of the order of 900-1800 kg.

The new tire on the same old rim no more than 200 grams heavier than the old one. That is approx. 0.02% heavier! Gimme a break! What engineering problems are our imaginations fantasizing about?

I have now driven 1500 km with the new tires. The ride quality is decidedly better notwithstanding the miniscule rise in unsprung weight.

And the car goes further with the same amount of fuel. For my volume of driving, I would exhaust four full tanks a month. Now I consume only three full tanks a month. How's that for change of fuel economy?

Larger wheels will probably result in better fuel economy, but what effect do you think it will have on the gear ratios? I mean take for example the reverse gear, which is generally weaker than the 1st and pulls slightly better than the 2nd. So, now on reversing up an incline, shall larger wheels result in loss of power?
Ram, have you come across something like this? I run stock rims and tires on my 2002 800. I have felt the car pretty underpowered trying to reverse up a steep incline.