We got so many questions regarding preparations of BMW for gravel rally that we decided to build the car, test it and pass the personal feedback. So the story of RacingDiffs crew at Rally Show Santa Domenica begins.
The car of choice
The choice came down to the car which was mentioned in your questions the most - BMW E36. In the lack of time, we took our friend's car which was already assembled for Autocross. However we had to do some modifications.
First we got AVO suspension shocks. This increased ride height for 2 inches, which was perfect for the event that we chosen. Long travel, reverse monotube shocks really changed the car drivability on the gravel super special stages. AVO suspensions offers single adjustable setup for just under 2000 EUR, which is perfect entry level setup. If you are planning to try out gravel rally, and this exceeds your budget, than you will end up frustrated and probably crash the car. This type of shocks are a must have and AVO suspension is the most cost-effective option on the market.
Than we built custom differential setup. The car was already equipped with a small case 168mm Limited slip diff. Since there was no time for big changes, we decided to keep the diff. We changed the gear ratio from 3.45:1 to 4.10:1. Since we kept the stock M50B20 engine, this allowed much faster corner exits from hair pins. LSD unit itself went through certain mods. It got equipped with our Stage 3 upgrade pack which includes: Billet steel cap to ensure it won't break, 4 clutch discs instead of factory 2 and multi-variation ramp plates set to 30°/60° angles. Asymmetrical ramp angles provide uneven lock on acceleration and deceleration. More aggressive lock is needed on throttle to ensure both wheels grab the surface with full capacity. This is really important on gravel rally as if the diff slips even slightly on corner exit, you will loose much time as 1 wheel doesn't have as close as enough traction to keep the car going. On the other hand, you need your diff to be less locked during engine breaking, to ensure smooth downshifts. You don't want your car to lock wheels while downshifting on the gravel surface, especially on RWD car. If you want to flick your car, than it's better to do it with hand brake, as it is more controllable.
Besides ramp angles, we installed 4 clutch pack which doubled the friction surface compared to the factory 2 clutch pack. This is important for 2 reasons:
1. Allows more lock capacity. For example, on 30° ramp angles, 2 clutch pack provides maximal 50% lock while 4 clutches provides almost 100% lock. We speak on full throttle of course.
2. Doubles the heat capacity. This provides much better wear resistance which is very important in racing usage. When plates are overheated, there is a change in performance. And you want your diff to be as consistent as possible during special stage. In extreme situations, like tire damage, this can save your life. Read until the end to find out what happened to us and how the diff helped us to finish the rally.
The event of choice
We have chosen the most respectable gravel rally show in this region - Santa Domenica Rally Show. This event is held near Zagreb in Croatia, every year on the last weekend of November. This is the 12th rally so far so it has a strong tradition. How respectable it is, tells the fact that ex Sébastien Ogier WRC spec Citroen C3 competed. A lot of R5 Skoda, Ford and Peugeot cars, R4 spec Mitsubishi Evo's, Subaru Impreza's etc. This is the favorite rally event of our friend Miroslav Mrgud Zrncevic, chief test driver at Rimac Automobili, who introduced us to this event in a first place.
Highlights from our journey
We attacked very strong from the SS1 leading the board with the time of 8 min 47 sec. Car felt really controllable with mods that we done, so we were relaxed and confident. Shocks provided excellent traction and the diff was perfect, so we started to push more and more.
In SS2 we came down to the jump too fast. The rear lower shock bolt snapped off. We were unable to finish the SS2, and according to the rule book we got the slowest time in division + 1 min. This really slowed us down. Luckily, the shock itself wasn't too damaged, so we managed to repair the car and continue.
However we didn't see the tire damage, so in SS3 the tire exploded. But we were determined not to give up this time! We continued driving with flat tire which got stuck to the body panel making the rim slip inside the tire. If we haven't had so strong Limited slip differential, we wouldn't be able to finish the rest (4,3km) of SS3. This brought us down to 4th place, so we were much disappointed.
We had to mount tires for Autocross which behaved as slicks on snow. Calculations said that we need to finish SS4 under 9 minutes to finish 3rd, which seemed quite incredible with a those tires and a broken shock absorber. But our motivation was just too strong. Not only we finished SS4 under 9 minutes, we set the day record of 8 min 34 sec, so we finished 3rd!
Our personal feedback
We have 2 conclusions for you guys:
1. Don't save money on shocks. Single adjustable, reverse monotube, long travel shocks with bypass valves are a must have. Our choice was AVO suspension as they had the best value for money ratio. Price was just under $2000. Don't go for cheap ebay alternatives. You will just end up frustrated.
2. High spec LSD is a must-have. As you already saw, thanks to properly set LSD unit, we managed to finish on the podium. This is where you make advantage over your competition.
If you need advice how to set your LSD unit for the Gravel rally, hill climb, circuit or any other discipline, please feel free to send us email and we will respond as soon as possible.
Happy (early) Valentine’s Day!
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